I don't think it's necessarily a bad thing or a red flag or that the person meant anything wrong by the gesture.. BUT I do think it's important to teach that if you EVER feel uncomfortable by that kind of thing, it's ok to say so and remove yourself from the situation.
I went to a small private school and our academic counselor was really huggy, our school is the type is pre-k to high school so more chances then not, he had known us basically our entire lives.
He never meant anything sexual or wrong with it, but when I was around that 12ish age, for some reason all of a sudden I didn't know what to do and hugging him made me uncomfortable. I said so and told my parents, we all spoke together and everyone got to explain their feelings.. he profusely apologized, my parents and I got to talk to him about it and get it all out in the open so it wasn't awkward and now, we laugh about it lol
just saying, regardless of the situation..there is nothing wrong with saying that you are uncomfortable and teaching kids what to do if they do feel that way.
It isn't burning bridges and in cases where it is just a misunderstanding, like mine was, getting it all out in the open helps things smooth over much faster and creates a safer school environment for all